Knowledge of patterns of genetic diversity enhances the efficiency of germplasm conservation and improvement. This study examined the organization of diversity for morphological and agronomic characteristics in 306 landraces of cultivated common bean (Phaseolus vulgaris L.) from Latin America and its relationship with phaseolin seed protein and allozyme diversity of the landraces. Data on pigmentation, growth habit, and leaflet, pod, seed, and phenology traits, as well as reaction to four important diseases and an insect pest, obtained from field evaluations at three locations in Colombia during the 1987-1988 cropping season, were analyzed by multivariate statistical analyses. In addition, these same 306 landraces were characterized by electrophoresis for phaseolin seed protein and nine allozymes. Results permitted separation of these landraces into Mesoamerican and Andean groups, confirming prior phaseolin and allozyme data. A marker-based multivariate analysis, using phaseolin or allozymes as an initial classification criterion, followed by a corroborating analysis of morpho-agronomic traits, suggested the existence of subgroups within each of the major Andean and Mesoamerican groups, with distinctive morphology, adaptation, and disease resistances. Molecular analyses in conjunction with morphological and agronomic evaluations of gene bank accessions are recommended, because these provide complementary information and increase the resolving power of genetic diversity analyses.

The inheritance of resistance to bean golden mosaic virus (BGMV) in common bean (Phaseolus vulgaris L.) was studied in crosses between susceptible bean variety XAN176 and resistant breeding lines 9236-6 (T446/A429) and 9245-94 (DOR303/T968). Disease response data were taken on plants from four generations derived from each cross (parents, F1, F2, and backcrosses (BCs) of F1 to both parents) at 25 days after plants were inoculated with BGMV, using whiteflies (Bemisia argentifolii Bellows & Perring) as vectors. The segregation ratios obtained from F2 and BC generations were consistent with the hypothesis that resistance in 9236-6, which prevents a chlorotic response, is conferred by a single recessive gene. The disease response in 9245-94 was controlled by two genes—a dominant gene controlling a dwarfing reaction and a recessive resistance gene preventing a chlorotic response to BGMV infection. An allelism test demonstrated that the gene controlling resistance in 9236-6 is nonallelic with the recessive gene controlling resistance in 9245-94. The gene symbol bgm is proposed for the recessive resistance gene (originally from A429) in 9236-6. The gene symbol bgm-2 is proposed for the recessive resistance gene (originally from DOR303) in 9245-94.

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Identification of superior yielding populations in early generations of common bean (Phaseolus mlgaris L.) would help eliminate poor populations, permit adequate sampling of promising populations, and save resources. Our objective was to determine the value of yield testing early generation bulks. Three checks and 33 populations were yield tested in a randomized complete‐block design with two replications at three locations in Colombia during three seasons. Each plot consisted of 4 rows; 3, 4, and 5‐m long in the F2, F3, and F4 generations, respectively. Data were taken on yield, seed weight, maturity, anthracnose, angular leaf spot, and common bacterial blight. Populations and locations were considered random and generations fixed effects. Differences were observed among populations for all traits. Effects of locations were significant (P < 0.01) for yield, seed weight, and maturity. Positive correlations (r) were found for yield between the F2 and F3, F2 and F4, and F3 and F4 at Popayán; and all r values except between the F2 and F4 were positive and significant (P < 0.05) at Palmira. No associations were found at Quilichao. When data were pooled over any two or all three locations, all but one r value were positive and significant (P < 0.05). Heritability estimates obtained by the regression of the F3 on F2 were 0.29 for yield, 0.61 for seed weight, and 0.47 for maturity. Predicted gain from selection (20% selection intensity) for yield in the F2 was 6.1% and actual gains in the F3 and F4 were 5.6 and 5.1%, respectively. Values for seed weight were >15% and for maturity <3%.

Toro et al. 1990).

Knowledge of parental combining ability is essential for creating useful genetic variation through hybridization. Our objectives were to examine combining ability for yield and its components for large‐seeded common bean (Phaseolus vulgaris L.) of Andean origin and to test an earlier observation that germplasms from Middle American races Durango and Jalisco possess positive general combining ability (GCA) for seed yield. Sixty‐four parents from different races and gene pools were randomly assigned to groups of 16. Within a group, eight parents were randomly chosen as females, the rest as males, and crossed in a Design II mating scheme. The resulting 256 F2 populations were evaluated in a reps‐in‐sets design with two replications at Palmira and Popayán, Colombia, in 1989. The experimental unit was a four‐row plot, 5 m long. The GCA effects using line × tester analysis were measured for seed yield (kg ha−1), pods per square meter, seeds per square meter, 100‐seed weight (g), and days to maturity. Mean squares due to males and females (vs. those for males × females) were larger in magnitude and significant (P < 0.05) for all traits; the smaller mean squares for males × females were significant only for seed weight and days to maturity. Mean yields of populations between races Durango and Jalisco were the highest, while populations between races Chile and Nueva Granada were the lowest. Populations between races Chile and Durango had the next‐lowest yields. Positive GCA effects were found for yield (19 parents), seed weight (6 of the 19), seeds per square meter (20), pods per square meter (19), and days to maturity (29). Negative GCA was found for days to maturity (25 parents).

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Additive genetic variance in large-seeded common beans {Phaseolus vulgaris L.), mostly of Andean South American origin, was higher than nonadditive variance for all traits. Heritability was 0.43 ± 0.19 for yield, 0.49 ± 0.20 for pods/m^ 0.63 ± 0.21 for seeds/m^ 0.76 ± 0.23 for 100-seed weight, and 0.55 ± 0.22 for days to maturity. Expected gain from selection (expressed in percentage of the population mean) was 9.2 for yield, 12.8 for pods/m^ 21.0 for seeds/m^, 17.6 for 100-seed weight, and 4.6 for days to maturity.